Viscosification and foaming of polyacrylamides

ABSTRACT

Embodiments of the invention relate to a method for treating a subterranean formation, comprising forming a fluid comprising polyacrylamide and a biopolymer and introducing the fluid to a subterranean formation wherein the polyacrylamide and biopolymer are selected to form the fluid with a longer foam half life and a higher viscosity than if only one polymer were selected. Embodiments of the invention relate to a method for treating a subterranean formation, comprising forming a fluid comprising polyacrylamide and a biopolymer and introducing the fluid to a subterranean formation wherein the polyacrylamide does not alter biopolymer crosslinking.

PRIORITY

This application claims priority to U.S. Provisional Patent ApplicationSer. No. 61/330,048, filed Apr. 30, 2010, entitled, “Viscosification andFoaming of Polyacrylamides,” and incorporated by reference herein in itsentirety.

FIELD

Embodiments of the invention relate to methods and compositions offluids for use in the oil field services industry. Specifically,embodiments relate to fluids containing polyacrylamide.

BACKGROUND

The constraints on gas handling capacity have resulted in shutting-in asignificant number of high gas-oil-ratio (GOR) wells. In most cases, theworkover objectives involve plugging the invaded gas zones to producefrom another zone and restore oil production. One major problem innaturally-fractured carbonates is the reduction of the crude oilproduction due to the water and gas breakthrough. Numerous solutionstake into account several parameters for gas shut off treatment design.Some of these parameters are: determination of the type of system thatfits best the well-reservoir conditions, treatment volume, averagefissure/fracture width and number of fissures to be plugged. However,another problem is the best placement technique for the sealing systemin the gas zone.

Few techniques have been developed to address the gas breakthrough innaturally-fractured carbonates, so it is a matter that has yet to bewidely discussed and researched.

The main challenges faced for gas and water shut-off treatments include:

-   -   Poor cement behind the production liner.    -   Low reservoir pressure and massive fractures resulting in loss        circulation.    -   Uncertainty with fracture volumes estimation.    -   Treatment execution under sub-hydrostatic conditions.

SUMMARY

Embodiments of the invention relate to a method for treating asubterranean formation, comprising forming a fluid comprisingpolyacrylamide and a biopolymer and introducing the fluid to asubterranean formation wherein the polyacrylamide and biopolymer areselected to form the fluid with a longer foam half life and a higherviscosity than if only one polymer were selected. Embodiments of theinvention relate to a method for treating a subterranean formation,comprising forming a fluid comprising polyacrylamide and a biopolymerand introducing the fluid to a subterranean formation wherein thepolyacrylamide does not alter biopolymer crosslinking.

FIGURES

FIG. 1 is a chart that shows foam half life and stability of 3.1 wt %acrylamide sodium acrylate copolymer (A1) with varying concentrations ofduitan gum and ammonium C6-C10 alcohol ethoxysulfate surfactant.

FIG. 2 is a chart that shows selecting the foaming agent (FormulationNo. 1 —3.1% A1+Acetic acid+crosslinker)+Foaming surfactant.

FIG. 3 is a chart that shows formulation No. 2 (5.2% A1+Ac+substitutedacrylamide polymer).

FIG. 4 is a chart that shows different acrylamide sodium acrylatecopolymer (A1) wt % concentrations—3.1%, 5.2% and 6%.

FIG. 5 is a chart for formulation No. 2 (5.2% A1+Ac+substitutedacrylamide polymer)+0.5 (vol) % surfactant D+0.5 (vol) % surfactant I.

FIG. 6 is a chart of polymer solutions foamed with 0.5% surfactant D.

FIG. 7 is a chart of formulation No. 1 (3.1% A1+Ac+substitutedacrylamide polymer+G1) with different hydration time after adding G1polymer.

FIG. 8 is a chart of formulation No. 1 with different concentration ofdiutan gum*.

FIG. 9 is a chart of rheology behavior on Fann-35 as a function of shearrate.

FIGS. 10A and 10B show G1 polymer effect on the setting time performanceof acrylamide sodium acrylate copolymer and substituted acrylamidepolymer fluids.

FIG. 11 is a series of photos showing in situ static foam pictures takenfrom left to right at 7 minutes, 1 hour and 3 hours in the view cell.

DESCRIPTION

At the outset, it should be noted that in the development of any suchactual embodiment, numerous implementation—specific decisions must bemade to achieve the developer's specific goals, such as compliance withsystem related and business related constraints, which will vary fromone implementation to another. Moreover, it will be appreciated thatsuch a development effort might be complex and time consuming but wouldnevertheless be a routine undertaking for those of ordinary skill in theart having the benefit of this disclosure. In addition, the compositionused/disclosed herein can also comprise some components other than thosecited. In the summary of the invention and this detailed description,each numerical value should be read once as modified by the term “about”(unless already expressly so modified), and then read again as not somodified unless otherwise indicated in context. Also, in the summary ofthe invention and this detailed description, it should be understoodthat a concentration range listed or described as being useful,suitable, or the like, is intended that any and every concentrationwithin the range, including the end points, is to be considered ashaving been stated. For example, “a range of from 1 to 10” is to be readas indicating each and every possible number along the continuum betweenabout 1 and about 10. Thus, even if specific data points within therange, or even no data points within the range, are explicitlyidentified or refer to only a few specific, it is to be understood thatinventors appreciate and understand that any and all data points withinthe range are to be considered to have been specified, and thatinventors possessed knowledge of the entire range and all points withinthe range.

The statements made herein merely provide information related to thepresent disclosure and may not constitute prior art, and may describesome embodiments illustrating the invention.

Embodiments of the invention create a seal in the gas producer zone totrap the gas, trying to avoid or minimize the damage in the crude oilproducer zone. Foaming a polyacrylamide-based water control system,becomes one of the best alternative to propose. However, as lab testinghas shown over time, polymers by themselves are not capable to maintaina stable foam before reaching the setting time of the system.

For that reason, after an extensive number of tests it has been foundthat the addition of a biopolymer to the hydrated polyacrylamideconsiderably increases the gel viscosity and the foam half life withoutaffecting the performance of the system before curing.

The polyacrylamide may include polyacrylamide, grafted polyacrylamide,modified polyacrylamide, polyacrylamide hybrids, hydrophobicpolyacrylamide, hydrophilic polyacrylamide, acrylamide sodium acrylatecopolymer, and/or any combination thereof. In some embodiments, thepolyacrylamide is selected for its molecular weight. In someembodiments, the polyacrylamide has a molecular weight of about 5 toabout 15 mM. In some embodiments, the polyacrylamide has a molecularweight of about 200 to about 500K.

The biopolymer may include diutan xanthan, guar and/or a combinationthereof.

In some embodiments, the biopolymer crosslinking is not altered by thepresence of the polyacrylamide. That is, the fluid has similar viscosityor other rheological properties it would have if no polyacrylimide.

In our lab, some tests have been carried out to evaluate the feasibilityof foaming the sealing gel system, which surges as one of the best waysfor placement of the sealing system in the gas producer zone. The foamedgel consists of a crosslinked polyacrylamide solution—in both the rigidand flowing versions—plus a surfactant, foamed in a mixer at high-shearrate. The foamed gel is created by means similar to those used foraqueous foam generation, where the major difference between foamed gelsand aqueous foams is that the external phase of the foamed gelcrosslinks, greatly enhancing the mechanical stability of the foamsystem. According to lab tests, the polyacrylamide maintains the foamstable for short time, so it becomes necessary the addition of a polymerthat aids in increasing the foam half life. Through a couple of labtests, it was found that polymer of different identity such as guar gumis capable of increasing the foam half life by increasing the viscosityof the crosslinked polyacrylamide solution without affecting theperformance of the setting time of the system. So far, on the flowinggel, it has been observed that the flowing gel is more robust when theguar gum is added into the crosslinked polyacrylamide solution.

One major problem of gas shut off is the placement of crosslinkedpolyacrylamide—such as acrylamide sodium acrylate copolymer and asubstituted acrylamide polymer gel is ensuring that the gel is injectedinto and stays in the gas-bearing zone, until set. For this reason,stable foam is required which requires the optimization of the foam halflife and foam quality to allow the system to set and prevent it slumpinginto the pay zone. It has proved difficult to create stable foam usingnitrogen with a polyacrylamide fluid and conventional foaming agents.However, by adding a second polymer to the fluid it is possible togreatly increase the foam half life and the viscosity of thepolyacrylamide solution. This is considered to be the result of thesecond polymer (guar or a biopolymer) greatly increasing the low shearapparent viscosity of the fluid. The increased low shear viscosityindicates a synergy between the polyacrylamide and the second polymer(Table 1 and 2).

TABLE 1 Viscosity and foam half life of Acrylamide Sodium AcrylateCopolymer (A1) with and without the addition of Guar (G1). FluidComposition - Viscosity (cP) 3.1 wt % 5.2 wt A1 + % A1 0.1 3.1 wt 0.2 wt5.2% wt 0.15 wt wt % 0.2 wt Shear Rate % A1 % G1 A1 % G1 G1 % G1  5.1sec−1 50 400 200 500 ~ ~ (cP) 10.2 sec−1 50 300 150 450 ~ 50 (cP)  170sec−1 36 126 150 279 6 18 (cP)  511 sec−1 36  91 133 211 4 12 (cP) FoamHalf  15′   82′ 36′31″   69′ 13′43″ 28′14″ Life

TABLE 2 Viscosity using Acrylamide Sodium Acrylate Copolymer (A1) withDiutan gum and Guar (G1) polymer Apparent viscosity 5.1 sec- 10.2 sec-170 sec- 511 sec- 1 (cP) 1 (cP) 1 (cP) 1 (cP) 3.1 wt % A1 50 50 36 363.1 wt % A1 + 0.2 wt % Guar 400 300 126 91 3.1 wt % A1 + 0.7 wt % 28001600 198 115 Diutan gum 3.1 wt % A1 + 0.42 wt % 1400 800 138 90 Diutangum 3.1 wt % A1 + 0.25 wt % 800 500 102 72 Diutan gum 0.42 wt % Diutangum 1400 800 60 25 0.25 wt % Diutan gum 600 350 27 13

Foamed fluids comprised of A1 with Diutan gum have a foam half lifegreater than five (5) hours. The most stable foam being when there isthe greatest degree of interaction between the two polymers (FIG. 1).

FIG. 1 shows the foam half life and stability of 3.1 wt % AcrylamideSodium Acrylate Copolymer (A1) with varying concentrations of Duitan gumand Ammonium C6-C10 alcohol ethoxysulfate surfactant.

1. 0.7 wt % Duitan gum+0.5 vol % Ammonium C6-C10 alcohol ethoxysulfatesurfactant

2. 0.7 wt % Duitan gum+1.0 vol % Ammonium C6-C10 alcohol ethoxysulfatesurfactant

3. 0.25 wt % Duitan gum+0.5 vol % Ammonium C6-C10 alcohol ethoxysulfatesurfactant

4. 0.42 wt % Duitan gum+0.5 vol % Ammonium C6-C10 alcohol ethoxysulfatesurfactant

Laboratory testing on foam has shown that the waring blender is not theappropriate equipment for foam generation since the mixing is notuniform with the highest shear occurring at the bottom of the blenderjar. For that reason, a Silverson mixer—L4RT model—was used for foamtesting, since a more uniform foam mixture is achieved as the mixerpaddle can move homogeneously throughout the foam.

The procedure for the foaming test is shown below:

Gel Mixing

-   -   Place the appropriate volume of water into the blender jar    -   Put the polyacrylamide (Acrylamide Sodium Acrylate Copolymer)        into the waring blender and start mixing at around 2000 rpm for        not less than one (1) hrs.    -   Add the activator and mix for 20 min and then add the        crosslinker and continue mixing for about 20 minutes.    -   The guar gum polymer is added as last additive and mixed for 1.5        hrs or 2 hrs. Through lab testing it has been demonstrated that        the right hydration of the polyacrylamide is very important for        the development of the viscosity of the lineal gel and        reproducibility of the results. Leaving the fluid        (polymer+activator+crosslinker) overnight has been the best way        to get better and reproducible results on the viscosity and the        foam half life.    -   It is a good practice to measure the viscosity for each        polyacrylamide and guar gum—crosslinked solution each time after        mixing

Foaming Testing in the Laboratory

-   -   Take 100 mL (101 g) of the crosslinked polyacrylamide solution        and put it into a graduated beaker (2000 mL) of polypropylene        and agitate on a magnetic stirrer.    -   Add the surfactant-foaming agent at the desired concentration to        the solution and mix for one (1) minute. In general, no foam is        generated on this stage    -   Mix the solution at 4000 rpm for 3 minutes, using a Silverson        Mixer—LV 4RTmixer. Try to get the full high shear around 15        sec±5 sec. The beaker should be rotated and moved up and down to        ensure uniform mixing.    -   Measure and record foam height based on the graduated scale on        the beaker    -   Measure the half-life of the foam (time required for 50 mL of        the liquid to drain off the foam after the mixer is shut off)        using a stop watch

Foam quality is calculated by using the following relationship:

Foam quality=(Foam Height−100 mL)/(Foam Height)*100%

Laboratory Results

TABLE 1 Formulations of the crosslinked Polyacrylamides - A1 (AcrylamideSodium Acrylate Copolymer) with (Hexamethylenetetramine) crosslinker andAcetic acid (Ac) pH control Fluid Water A1 crosslinker Acetic acidsystem (%) wt % wt % (Ac) wt % 1 96.2 3.1 0.21 0.21 2 94.0 5.2 0.21 0.213 90.1 6.0 0.21 0.21

TABLE NO. 2 Evaluation of Foaming surfactants and stabilizers with aAcrylamide Sodium Acrylate Copolymer (A1) with Hexamethylenetetraminecrosslinker and Acetic acid (Ac) pH control A1(%) + Vol. Fluid Ac +Foaming surfactants (vol %)* Initial Foam Quality of system Crosslinerand polymer stabilizers (wt %)* Vol (cc) Volume (cc) Half-Life Foam (%)1 3.1 D (0.5%) 100 650 15′ 84.6 2 3.1 D (1%) 100 1000 17′ 90.0 3 3.1 D(2%) 100 1220 16′07″ 91.8 4 3.1 AEP (0.5%) 100 800 15′51″ 87.5 5 3.1 AEP(1%) 100 1180 16′15″ 91.5 6 3.1 AEP(0.75% + D (0.25%) 100 1180 16′00″91.5 7 5.2 D (0.5%) 100 320 36′31″ 68.8 8 5.2 D (1%) 100 550 34′00″ 81.89 5.2 B (1%) 100 550 31′45″ 81.8 10 5.2 B (2%) 100 250 18′12″ 60.0 115.2 D (1%) + I(1%) 100 12 5.2 D (0.5%) + I(0.5%) 100 350 36′23″ 71.4 135.2 AEP(0.5%) + I(0.5%) 100 375 26′00″ 73.3 14 5.2 D (0.5%) + I(0.5%) +0.15 wt % G1 300 69′27″ 66.7 15 5.2 D (0.5%) + I(0.5%) + 0.05 wt % 100320 53′00″ 68.8 G1 16 6   D (0.5%) 100 300 50′00″ 66.7 17 3.1 D (0.5% +I(0.5%) + 0.24 wt % G1 100 300 73′43″ 66.7 18 3.1 0.24 wt % G1 + 0.5% D100 375 82′31″ 73.3% 19 3.1 Same as #18 @ 180° F. 100 375 37′09″(

) 73.3% 20 — 0.12 wt % G1 + 0.5% D 100 1150 12′43″ 91.3 21 — 0.12 wt %G1 + 1% D 100 1200 11′38″ 91.7 22 — 0.24 wt % G1 + 0.5% D 100 100026′14″ 90 23 3.1 Same as test #18 with 30 min 100 375 70′ 73.3 hydrationG1 24 3.1 Same as test #18 13 hrs after 100 375 95′ 73.3 addition of G125 3.1 0.24 wt % G1 + 2% C 100 200 55′ 50 26 3.1 0.24 wt % G1 + 5% C 100300 171′ 66.6 27 3.1 0.24 wt % G1 + 10% C 100 300 125′ 66.6 28 3.1 0.24wt % G1 + 1% D + 3% C 100 200 20′ 50 29 3.1 0.24 wt % G1 + 1% MS + 1% D100 280 37′ 64.2 30 3.1 0.24 wt % G1 + 1% MS + 2% C 100 350 85′ 71.4 313.1 0.24 wt % G1 + 1% F 100 300 65′ 66.6 *Description of foamingsurfactants and stabilizers used AEF: Alcohol Ether Phosphate A =Ethoxylated branched C11-14, C13-rich alcohols and Ethoxylated4-nonylphenol B = Cocamidopropyl Betaine C = Dicoco Dimethyl AmmoniumChloride D = Ammonium C6-C10 alcohol ethoxysulfate E = Linear/BranchedC11 Alcohol Ethoxylate (8 EO) F = Amphoteric alkyl amine G = Sodiumtridecyl ether sulfate H = Mixture of Ethoxylated alcohols I = Mixtureof Polyglycols, Oxyalkylates, and Methanol MS = Mutual Solvent G1 = Guarpolymer Testing with: water + 1% SA1 + 0.2% crosslinker + 1.8 vol %Phenyl Acetate + 0.3 vol % Ac + 5 gpl D Vol. Foam H. No. Vol. Fluid1Foam (cc) Life Foam Quality (%) 31 100 720 36′40″ 86 32 Con 0.24 wt % G1100 475 100′ 78.9 (Hexamethylenetetramine) crosslinker and Acetic acid(Ac) pH control

indicates data missing or illegible when filed

SA1 Substituted Acrylamide Polymer—

Below are some graph that simplify the obtained results

The FIGS. 2 and 3, show that the foam is more stable with the SurfactantD and that it is not necessary to increase its concentration above 0.5vol % FIG. 2: Selecting the foaming agent (Formulation No. 1 —3.1%A1+Acetic acid+crosslinker)+Foaming surfactant

FIG. 3: Formulation No. 2 (5.2% A1+Ac+substituted acrylamide polymer).

TABLE 3 here Fluid Composition - Viscosity (cP)

fluid nucleus

0.12 wt % G1 0.5% D surfactant 0.24 wt % G1 + 6.9% D

5.2% A1

3.2% A1 + 80° F. 80° F. 71° C.

3.1%

3.1%/A1 +

5.2% 0.18 wt % 0.05 wt %

6% Formed Formed Formed Shear Rate A1 0.24 wt % G1 A1 G1 G1 A1 Linealfluid Lineal fluid fluid  5.1 sec−1 (cP) 50 400 200 500 200 200 ~ 300 ~500 400 10.2 sec−1 (cP) 50 300 150 450 250 450 ~ 250 50 600 350  170sec−1 (cP) 36 126 150 279 204 378 6 108 18 153  84  511 sec−1 (cP) 36 91 133 211 165 216 4  64 12  72  41 Foam Half Life  15′   82′ 36′31″  69′   53′   30′ 13′43″ ~ 28′14″ ~ ~

indicates data missing or illegible when filed

TABLE 4 here

L400 + HE1 1 h 2 h 3 h 13 h  5.1 sec−1 (cP) — 100 300 400 550 500 400200 550 600 600 600 10.2 sec−1 (cP) — 100 250 300 350 300 250 125 350450 450 491  170 sec−1 (cP) 15  69 120 120 129 129  98  90 150 165 165165  511 sec−1 (cP) 10  56  85

 95  93  76  68 101

115 115 Foam IL-Life — — — — — — —

— — —

indicates data missing or illegible when filedFIG. 4 is a chart that shows different acrylamide sodium acrylatecopolymer (A1) wt % concentrations—3.1%, 5.2% and 6%. Increasing thepolyacrylamide concentration decreases foam quality but increases foamhalf life

FIG. 5 is a chart for formulation No. 2 (5.2% A1+Ac+substitutedacrylamide polymer)+0.5 (vol) % surfactant D+0.5 (vol) % surfactant I.This shows increased concentrations improves foam stability burdecreases slightly the foam quality.

FIG. 6 is a chart of polymer solutions foamed with 0.5% surfactant D.Good foam quality and poor foam stability for both the linear gel withG1 (guar) and for A1(Acrylamide Sodium Acrylate Copolymer). However whenboth polymers (Acrylamide Sodium Acrylate Copolymer+Guar) are combinedthe foam stability increases.

FIG. 7 is a chart of formulation No. 1 (3.1% A1+Ac+substitutedacrylamide polymer+G1) with different hydration time after adding G1polymer.

FIG. 8 is a chart of formulation No. 1 with different concentration ofdiutan gum*.

FIG. 9 is a chart of rheology behavior on Fann-35 as a function of shearrate.

The hydration level of both polymers plays a very important role forfoam stability. Better and more reproducible results are achieved whenthe polyacrylamide solutions is hydrated for extended period of timeprior to adding the G1 guar polymer.

FIGS. 10A and 10B show G1 polymer effect on the setting time performanceof acrylamide sodium acrylate copolymer and substituted acrylamidepolymer fluids. No major change was seen. Reaching the hard Set Time ofboth system was faster upon addition of G1. Also, the gel looked morerobust when G1 was included in the formulation.

Photos of 3.1 wt % Acrylamide Sodium Acrylate Copolymer and 1 wt %Acrylamide Sodium Acrylate Copolymer illustrate the performance.

Foaming Evaluation with Diutan Gum

Base fluid 3.1 wt % A1+0.21 wt % substituted acrylamide polymer+0.21 wt% Ac+0.5 vol % D

FIGS. 8 and 9 show how the rheology is depending of the polymer orpolymer combination used. The +symbol mean that the fluid containsA1+substituted acrylamide polymer+Ac+Surfactant D at the concentrationshown above. FIG. 8 shows results for Formulation No. 1 with differentconcentration of Diutan gum* and FIG. 9 shows results for Rheologybehavior on Fann-35 vs Shear rate.

High foam stability with the addition of the Diutan gum. 5 hrs with notdrainage observed.

-   -   *Concentrations of Diutan gum and surfactant    -   1. Base fluid+0.7 wt % Duitan gum+0.5 vol % Ammonium C6-C10        alcohol ethoxysulfate surfactant    -   2. Base fluid+0.7 wt % Duitan gum+1.0 vol % Ammonium C6-C10        alcohol ethoxysulfate surfactant    -   3. Base fluid+0.25 wt % Duitan gum+0.5 vol % Ammonium C6-C10        alcohol ethoxysulfate surfactant    -   4. Base fluid+0.42 wt % Duitan gum+0.5 vol % Ammonium C6-C10        alcohol ethoxysulfate surfactant

Setting Time of Acrylamide Sodium Acrylate Copolymer when Adding DiutanGum

No much difference on the setting time with and without Diutan. However,the Diutan impart elasticity on the consistency of the system. Thepicture with Diutan shows how the bubbles are after the system reachesits hard set time, not fluid drainage.

Evaluation of Surfactants with Diutan Gum and a Acrylamide SodiumAcrylate Copolymer

Composition (Active Components) of Surfactants

Base fluid formulation: 3.1 wt % Acrylamide Sodium Acrylate Copolymer +0.21 wt % substituted acrylamide polymer + 0.53 wt % Acetic acid +Diutan gum variable Test Diutan Foam Vol. Initial Foam Foam Quality No.wt % agent % BVol (cc) Volume (cc) Half-Life (%) 1  0.8 gpb D 0.5% 100280 18 hrs = 0 cc 64 2 0.42 wt % D 0.5% 100 355 5 hrs = 0 cc 71.8 14 hrs= 47% 3 0.25 wt % D 0.5% 100 390 5 hrs = 0 cc 74.4 14 hrs = 67% 4 0.25wt % C   5% 100 300 2.5 hrs 66 5 0.25 wt % C   2% 100 350 1 h45′ 71.4 60.25 wt % C   2% + 100 260 1 h15′ 61.5 MS 7 0.25 wt % A 0.5% 100 170 — 80.25 wt % A   2% 100 300 5 hrs = 30% 66 9 0.25 wt % F 0.5% 100 220 6 hrs= 0 cc 54.5 10 0.25 wt % F   2% 100 360 6 hrs = 25% 72.2 11 0.25 wt % F0.5% 100 350 6 hrs = 0 cc 71.4 12 0.25 wt % B 0.5% 100 250 — 63.0 130.25 wt % B   2% 100 490 5 hrs = 0 79.6 7 hrs = 40% 14 0.25 wt % B   1%100 350 5 hrs = 0 71.4 7 hrs = 30% 15 0.25 wt % E 0.5% 100 180 — 44.4 160.25 wt % G 0.5% 100 180 — 44.4 Base fluid formulation: 3.1 wt %Acrylamide Sodium Acrylate Copolymer + 0.21 wt % substituted acrylamidepolymer + 0.53 wt % Acetic acid + 0.25 wt % Diutan gum contaminated withCantarell Crude Oil Vol. Foam Foam Initial Foam Volume Quality Crude (%)agent % BVol (cc) (cc) (%) Half-Life 18 5 D 0.5% 100 390 74.4 20 min =60% 19 5 F   2% 100 370 73.0 1.5 hrs = 45.2% 20 5 G 0.5% 100 370 73.0 6hrs = 70% 7 hrs = 68% 21 10 G 0.5% 100 370 73.0 2 hrs = 70.3 4 hrs =60.7 5 hrs = 52.2 22 15 G 0.5% 100 340 70.6 4 hrs = 70.6 5.5 hrs = 23 235 B 2 100 500 80.0 3 hrs = 78.4 4 hrs = 58 24 10 B 1 100 350 71.4 0 hrs= 70.6 6 hrs = 70.6 25 20 B 1 100 340 70.6 7 hrs = 70.6 8 hrs = 62.5 A =Ethoxylated branched C11-14, C13-rich alcohols and Ethoxylated4-nonylphenol B = Cocamidopropyl Betaine C = Dicoco Dimethyl AmmoniumChloride D = Ammonium C6-C10 alcohol ethoxysulfate E = Linear/BranchedC11 Alcohol Ethoxylate (8 EO) F = Amphoteric alkyl amine G = Sodiumtridecyl ether sulfate H = Mixture of Ethoxylated alcohols

Foam Stability at Temperature

A fluid formulated as follows 3.1 wt % Acrylamide Sodium AcrylateCopolymer+0.7 wt % Diutan gum+1.0 vol % Cocamidopropyl Betaine wasevaluated further in a circulating foam loop at 100° C. using nitrogen.The hexamethylenetetramine was not included to prevent gelation duringthe test. The foam was formulated at a quality of 72%. A constant shearrate of 100 s⁻¹ was maintained throughout the test except for threeshear ramps where the shear rate was reduced to 75, 50 25 and thenincreased to 50, 75 and 100 s⁻¹. Table 1 shows the calculated power lawparameters, for the foam versus elapsed time. Clearly the foam maintainsits viscosity and its shear thinning properties with only minor changesover the test time of 3.5 hours. The rheology trace is included in FIG.11. Pictures of the foam segregated in a view cell are shown in FIG. 11.In situ static foam pictures taken from left to right at 7 minutes, 1hour and 3 hours in the view cell. FIG. 11. In situ static foam picturestaken from left to right at 7 minutes, 1 hour and 3 hours in the viewcell. No drainage was seen during the 3.5 hour test time. No drainagewas seen during the 3.5 hour test time.

Some coarsening of the foam is evident, but the foam has no drainageover the 3.5 hour test time.

TABLE 1 Power law parameters for foam test Elapsed Time, Temperature,hr:min:sec ° C. n′ K′, R² 1:14:32 100.3 0.435 0.0120 0.977 2:28:36 101.20.449 0.0974 0.987 3:25:40 101.3 0.456 0.0888 0.992

The preceding description has been presented with reference to someillustrative embodiments of the Inventors' concept. Persons skilled inthe art and technology to which this invention pertains will appreciatethat alterations and changes in the described structures and methods ofoperation can be practiced without meaningfully departing from theprinciple, and scope of this invention. Accordingly, the foregoingdescription should not be read as pertaining only to the precisestructures described and shown in the accompanying drawings, but rathershould be read as consistent with and as support for the followingclaims, which are to have their fullest and fairest scope.

Furthermore, none of the description in the present application shouldbe read as implying that any particular element, step, or function is anessential element which must be included in the claim scope: THE SCOPEOF PATENTED SUBJECT MATTER IS DEFINED ONLY BY THE ALLOWED CLAIMS.Moreover, none of these claims are intended to invoke paragraph six of35 USC §112 unless the exact words “means for” are followed by aparticiple. The claims as filed are intended to be as comprehensive aspossible, and NO subject matter is intentionally relinquished,dedicated, or abandoned.

1. A method for treating a subterranean formation, comprising: forming afluid comprising polyacrylamide and a biopolymer; and introducing thefluid to a subterranean formation; wherein the polyacrylamide andbiopolymer are selected to form the fluid with a longer foam half lifeand a higher viscosity than if only one polymer were selected.
 2. Themethod of claim 1, wherein the polyacrylamide comprises polyacrylamide,grafted polyacrylamide, modified polyacrylamide, polyacrylamide hybrids,hydrophobic polyacrylamide, hydrophilic polyacrylamide, acrylamidesodium acrylate copolymer, and/or any combination thereof.
 3. The methodof claim 1, wherein the polyacrylamide is selected for its molecularweight.
 4. The method of claim 3, wherein the polyacrylamide has amolecular weight of about 5 to about 15 MM.
 5. The method of claim 3,wherein the polyacrylamide has a molecular weight of about 200 to about500K.
 6. The method of claim 1, wherein the biopolymer is diutan.
 7. Themethod of claim 1, wherein the biopolymer is xanthan.
 8. The method ofclaim 1, wherein the biopolymer is guar.
 9. The method of claim 1,wherein the biopolymer crosslinking is not altered by the presence ofthe polyacrylamide.
 10. A method for treating a subterranean formation,comprising: forming a fluid comprising polyacrylamide and a biopolymer;and introducing the fluid to a subterranean formation; wherein thepolyacrylamide does not alter biopolymer crosslinking.
 11. The method ofclaim 10, wherein the polyacrylamide comprises polyacrylamide, graftedpolyacrylamide, modified polyacrylamide, polyacrylamide hybrids,hydrophobic polyacrylamide, hydrophilic polyacrylamide, acrylamidesodium acrylate copolymer, and/or any combination thereof.
 12. Themethod of claim 10, wherein the biopolymer is diutan.
 13. The method ofclaim 10, wherein the biopolymer is xanthan.
 14. The method of claim 10,wherein the biopolymer is guar.
 15. The method of claim 10, wherein thepolyacrylamide is selected for its molecular weight.